Semiconductor wafer manufacture includes processes by which thin films or layers of material are built up and etched on the surfaces of wafer substrates, usually in vacuum processing chambers where materials are deposited or etched by chemical or plasma processes. One of the greatest causes of losses in the manufacture of semiconductors is contamination by minute particles. With the trend toward increased miniaturization in semiconductor design, the presence of a particle on the surface of a wafer can render an entire device inoperative. Accordingly, control of particle production in manufacturing processes is continually increasing in importance.
In vacuum processes, particularly deposition processes, in which material vapors result in the formation of coatings on chamber walls and other internal reactor parts that are in contact with the processing medium, the build up and eventual flaking of the coatings is a major source of contamination of semiconductor wafers by particles. Reduction of the tendency for such deposits to flake is thus a major goal of processing equipment and process design. Chamber shields that are employed to intercept deposits from forming on permanent chamber surfaces become particle sources that are a focus of particle contamination prevention efforts. Frequent replacement and cleaning of such shields is a solution to the flaking problem, but such a solution itself subtracts from the productivity of the processing equipment and manufacturing process. Accordingly, ways to use such shields in a way that increases their ability to retain deposits for longer times without flaking are constantly needed.
Making chamber shields more resistant to flaking has included efforts to condition the surfaces of shields to increase the adhesion of the deposits that they collect. Still, flaking occurs eventually if the shields are not frequently removed or cleaned. Process conditions have been observed as aggravating the flaking phenomenon. Mechanical contact, gas flow, and pressure and thermal cycling of parts are among the parameters that cause the coatings to flake off of the shields.
Accordingly, needs remain for ways to improve the ability of shields in semiconductor wafer processing chambers to retain deposits without flaking.